1. Field of the Invention
The present invention relates to a stratified-combustion internal combustion engine, in which an air-fuel mixture and air, for example, are individually supplied to a combustion chamber, and the air-fuel mixture is burned in the combustion chamber in a manner such that the air-fuel mixture and the air form a stratified swirl flow.
2. Description of the Related Art
According to stratified-combustion internal combustion engines of this type, a rich air-fuel mixture and air is supplied to a combustion chamber, and the air-fuel mixture is subjected to perfect combustion by igniting the rich air-fuel mixture. In these internal combustion engines, therefore, the air-fuel mixture can be burned even if the total air-fuel ratio of the mixture and the air is higher than the theoretical air-fuel ratio, that is, if the air-fuel mixture is lean as a whole. Accordingly, the fuel cost performance of the engine can be improved, harmful materials, for example CO, NO.sub.x etc., contained in the exhaust gas of the engine can be reduced, and the engine can be effectively prevented from knocking.
In the stratified-combustion internal combustion engines, the combustion of the air-fuel mixture in the combustion chamber is effected through the aforementioned unique procedure. Thus, the improvement of the internal combustion engines of this type is intended primarily to produce a rich air-fuel mixture in the vicinity of an ignition plug in the combustion chamber, and secondarily to activate the air-fuel mixture flow in the combustion chamber, that is, to increase the combustion speed after the ignition, thereby stabilizing the combustion and enhancing the efficiency of combustion.
Accordingly, the conventional stratified-combustion internal combustion engines use various means for producing a rich air-fuel mixture layer on the ignition-plug side, and an air layer, that is, a lean air-fuel mixture layer, on the piston side, in the combustion chamber of one cylinder. One such means will be described in connection with an internal combustion engine which has two intake ports on one side of the combustion chamber of each cylinder. In the engine of this type, the intake ports are connected to a common intake passage by means of branch passages, and a swirl control valve is disposed in the branch passage which connects with one of the intake ports. In a part load condition, that is, a operation condition in which the fuel cost performance is more important than the power of the engine, the swirl control valve closes the branch passage corresponding to the one intake port, so that air is first introduced into the combustion chamber through the other intake port only. As a result, a swirl flow of air turning around the axis of the cylinder is produced in the combustion chamber. In the second half of the intake stroke, thereafter, fuel is supplied to the combustion chamber. If the air and the air-fuel mixture are introduced into the combustion chamber of this manner, the air-fuel mixture in the combustion chamber can be divided into two layers, rich and lean, as mentioned before.
Since the aforementioned means requires the swirl control valve to be disposed in one of the branch passages, however, the construction of the internal combustion engine itself is complicated, and the intake air is obstructed by the swirl control valve itself in the operation condition that the swirl control valve is opened, that is, in the full opening throttle condition. Therefore, the power of the engine is decreased.